Small objects such as keys, eyeglasses, remote control units for TVs and VCRs are readily misplaced. It is known in the art to attach to such objects a detector unit that can emit an audible beeping signal when a definitive pattern of human-generated audible whistles, hand claps, or the like is heard. The recognizable patterns of human-generated sounds, hand claps for example, are termed desired actuation sounds.
Typically the detector unit includes a microphone, waveform shapers, electronic timers, a beeping sound generator, and a loudspeaker. The microphone is responsive to audible sound, which can include the desired actuation sounds as well as ambient noise, and commonly a piezoelectric transducer functions as both the microphone and the loudspeaker. The waveform shapers attempt to discriminate between waveforms resulting from desired actuation sounds, and waveforms from all other sounds. The waveform shaper output signals are coupled to electronic timers in an attempt to further discriminate between desired actuation sounds and all other microphone detected sounds. Ideally, the detector unit provides a beeping signal into the loudspeaker only when the desired searcher-generated actuation sounds are detected. The loudspeaker beeping is a locating signal that enables a user to locate the objects attached to the detector unit from the beeping sound.
Unfortunately, prior art detector units tend to not respond at all, or to false trigger too frequently. By false trigger it is meant that the units may output the beeping sound in response to random noise, human conversation, dogs barking, etc., rather than only in response to desired human-generated actuation sounds. One approach to minimizing false triggering is to design the detector unit to recognize only a specific pattern of desired actuation sounds, for example, a series of hand claps that must occur in a rather rigid timing pattern.
U.S. Pat. No. 4,507,653 to Bayer (1985), a simplified version of which is shown in FIG. 1A, typifies such detector units. Referring to FIG. 1A, a Bayer-type detector unit 10 may be coupled by a cord, a key ring or the like 20 to one or more objects 30, e.g., keys. Ideally, unit 10 responds to audible activation sounds 40 generated by a human user (not shown), and should not respond to noise or other sounds. When the desired activation sounds are present, unit 10 should output audible sound 50, which alerts the user to the location of the objects 30 affixed to the unit. Otherwise, unit 10 should not output any sounds.
As disclosed in the Bayer patent, unit 10 includes a microphone-type device 60 that responds to ambient audible sound (both desired activation sounds and any other sounds that are present). These transducer-received analog sounds are shown as waveforms A in FIGS. 1A, 1B-1 and 1C-1. In FIGS. 1B-1 and 1C-1, waveforms representing four hand claps (or similar sounds) are shown. By way of example, in FIG. 1B-1, the first two hand claps occur closer together in time than do the first two hand claps in FIG. 1C-1. These waveform A signals are amplified by an amplifier 70, whose output is coupled to a Schmitt trigger unit 80. The Schmitt trigger unit compares the magnitude of the incoming waveforms A against a threshold voltage level, V.sub.THRESHOLD. When waveform A exceeds V.sub.THRESHOLD, the Schmitt trigger outputs a digital pulse, shown as waveform B in FIGS. 1A, 1B-2, 1C-2.
The Schmitt trigger digital pulses are then input to an envelope shaper 90 that provides a rectifying function. If the Schmitt trigger digital pulses (waveform B) are sufficiently close together, e.g., &lt;125 ms or so, the envelope shaper output will be a single, longer-duration, "binary pulse". These binary pulses are shown as waveform C in FIGS. 1A, 1B-3, and 1C-3. Collectively, the Schmitt trigger and envelope shaping are intended to help unit 10 discriminate between desired activation sounds and all other sounds.
The start of a binary pulse is used in conjunction with digital timer-counter units, collectively 100, and latch units, collectively 110, to generate various predetermined time periods. Bayer relies upon a first predetermined time period, which is shown as waveform D in FIG. 1A, 1B-4 and 1C-4, to determine whether desired activation signals have been heard by microphone 60. Waveform D will always be a fixed first predetermined time period T.sub.p-1, for example, 4 seconds. Per the '653 patent, if four binary pulses occur within that fixed first predetermined time, unit 10 will cause an audio generator 120 to output beep-like signals to a loudspeaker 130. (In practice, Bayer's loudspeaker 130 and microphone 60 are a single piezo-electric transducer.)
Even though the user-generated activation sounds must adhere to a predetermined pattern, Bayer-type units still tend to false trigger by also beeping in response to noise, conversation, etc. For example, although the time separation of various waveforms A in FIGS. 1B-1 and 1C-1 differ, each waveform set results in four binary pulses occurring within the time period T.sub.p-1, and beeping results in both cases. Thus, Bayer-type units do not try to discriminate against noise sounds by examining and comparing patterns associated with pairs of hand claps. Instead, discrimination between noise and user-activation sounds is based upon rather static timing relationships designed and built into the unit.
Further, Bayer-type units can be difficult to use because the properly timed sequence of activation sounds, e.g., claps, must first be learned by a user. Unless the user learns how to clap in a proper sequence that matches the static signal recognition inherent in Bayer's detector unit, the unit will not properly activate and beep. Indeed, Bayer provides a built-in visual indicator to assist a user in learning the properly timed hand clapping sequence.
Even if prior art detector units can be made to operate properly, it will be appreciated that generated beep-like audio tones may not readily allow a user to locate the unit. Users generally have more experience in successfully locating the origin of an audible locating signal that is a human voice, rather than a beep-like tone. Further, in generating an audible locating signal, prior art devices ignore users who may be hearing impaired, or who could nonetheless benefit from a locating signal that was visual and/or audible.
Thus, there is a need for a detector unit having improved response to desired user-generated activation sounds, while not responding to other sounds. Such unit should not unduly comprise between timing constraints that improve immunity to false triggering, and ease of generating desired activation sounds. In discerning between incoming sounds to decide whether to output a locating signal, preferably such unit should adapt dynamically to a user's pattern of activation sounds, rather than force the user to learn a static sequence of such sounds. Finally, the unit should be usable by any user, and not be dedicated to a single user. Preferably such unit should provide capability to generate a locating signal that is visual and/or audible, and if audible, a locating signal that can include a human voice. Further, such unit should provide good signal recognition, even in the presence of high magnitude ambient noise.
The present invention provides such a detector unit, and a method of adaptively recognizing desired actuation sounds, such as hand claps.